Function of the Color Filters – Reflection Densitometer

Posted: September 21, 2012 in Color, Density filters, FOGRA, Ihara, INK, ISO 12647-2, ISO Press standardisation, PDF
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Color reflection densitometers such as Ihara R730 are equipped with  color filters to deliver density values for the specific process colors Cyan, Magenta, Yellow and Black. For each of the colors Cyan, Magenta and Yellow a specific filter is used which reflects the spectral characteristics of the respective ink.

Fig. 1 shows the remission curves of the solid tones of Cyan, Magenta, Yellow and for Paper White. Remission is the term for the degree of reflectance at a certain wavelength. The remission curve describes the reflectance among the entire visible spectrum and is a unique description for the color.

Fig. 1: The remission curves of the process colors Cyan,Magenta and Yellow and for Paper White.

The solid (optical) density is linear to the amount of ink applied and therefore a valid method for controlling the quality of printwork. Depending on the solid density, the shape of the remission curve changes. As seen in an example in Fig. 2 for three different densities in Cyan the changes are the largest at remission values beyond 590 nm (red).

This is why densities for Cyan are measured with a red filter with a spectral transmittance peak at 600 nm. The Cyan sensor (which consists of a photoelement with a red-sensitive filter in front) just detects the red portion of light and will be susceptible to small changes in Cyan density.

Fig. 2: Example for the remission curves for different densities for Cyan. The density measurement is carried out with a red filter, where changes in remission are susceptible.

Respectively, Yellow is measured with a blue filter at 430 nm and the process color Magenta is measured with a green filter at 530 nm wavelength.  Each process color is detected with its complementary filter:

• Cyan with a red filter

• Magena with a green filter

• Yellow with a blue filter.

The black color could be measured with any (or with no) filter, because its remission is even along the entire spectrum. To achieve a standardized density value, a filter called V is used which reflects the visual gray sensitivity.

 About Ihara R730:

 The Ihara R730 Colour Reflection Densitometer is a sophisticated QC tool. It has all of the measuring functions possible with a densitometer for full analysis of process work.

For a sophisticated densitometer with every possible function for measuring process work, then you need the Ihara R730 – you won’t find better value or a more accurate instrument! Simple operation means it is still fine for basic press control, but the extra features will help you detect and sort out just about anything that can possibly go wrong!

Not only does the R730 allows you to measure tints, and enable you to achieve a consistent ink densities on press, but the wide range of measuring functions available is ideal for QC departments, as well as sorting out printing problems.

  • Top Performance & Reliability  Made in Japan by Ihara Electronic Industries, the R730 has proven reliability and accuracy.
  • Menu Driven Commands  Simply select the required functions from the on-screen menu – you won’t ever need to read a manual. Clear and precise instructions for every measurement are displayed on the large LCD screen.
  • Help Key  Displays explanations for all measuring functions, along with answers to FAQs.
  • Quick Calibration  Recalibrate the unit in seconds.
  • Auto Function  Automatically measures density or dot gain.
  • Printer & Computer Interface  Configurable RS 232 serial interface provided for connecting to a PC or printer.
  • Fully Portable  Rechargeable batteries provide up to 4,000 readings before recharging.
  • Plate Reading  Optimized function for checking control strip tints on plates – available at small extra cost.
  • Filter/Aperture Options  Standard models supplied with Status T filters, 3 mm aperture and polarized. Manufacturer’s options available for Status E filters, 1.7 mm aperture and no polarization.

    Ihara Densitometer R730 – The best in class

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